Microelectronic devices are widely used and are becoming smaller in dimensions as well as more complex. Manufacturing of such microelectronic devices requires accurate inspection and metrology to identify appropriate patterns on substrates (e.g. wafer substrates), as well as identify defects in such patterns. Generally, the structure's properties (geometry and material composition) can be determined by analyzing the optical response of the structure at different wavelengths, different polarization states and/or different directions.
Accurate characterization of the geometrical and material properties of microelectronic devices becomes increasingly challenging, as the critical dimensions become ever smaller and the devices become more complex. Optical reflectometry (including spectral reflectometry and spectral ellipsometry) is an extremely effective method for obtaining information on the geometry and material properties of such structures. In this method, broadband light is shone on a sample and collected after being reflected from it. By analyzing the specular reflectance of different wavelengths and polarization components of the incident light, incident at different directions, it is possible to obtain information about the structure/sample. Commonly, optical reflectometry is applied to test structures comprised of a repeating array of identical elements, e.g. grating.
Metrology is commonly used to identify specific attributes of the measured structure, such as geometric parameters or material characteristics, and typically utilize spectral measurements. The accuracy by which these parameters can be measured is directly determined by their effect on the measured spectra.